Although asbestos is carcinogenic and induces both bronchogenic carcinomas and pleural and peritoneal mesotheliomas in humans, the underlying mechanisms of fiber carcinogenesis are not known. During the previous funding period, the applicant has shown, and for the first time, that asbestos fiber is a potent gene and chromosomal mutagen in mammalian cells and induce mostly large multilocus deletions. These findings provide the first direct link between chromosomal abnormalities that have frequently been demonstrated in vitro and carcinogenicity in vivo. To extend these findings and to examine how asbestos induces mutations, particularly the role of reactive oxygen species, the applicant proposes a series of seven specific aims to address three testable hypotheses using the human-hamster hybrid (AL) cell model. The first objective is to determine if oxyradicals, particularly hydroxyl radicals, generated by chrysotile asbestos result in oxidative DNA damages and mutagenesis in AL cells. The induction of the oxidative DNA damaged product, 8-hydroxl-2-'deoxyguanosine and the formation of hydoxyl radicals will be determined from fiber-treated cultures using HPLC-EC and the salicylate assays respectively. To show that oxyradicals induced by chrysotile fibers actually mediate the mutagenic events, the incidence and types of SI mutants induced by equitoxic doses of either asbestos fibers or hydrogen peroxide (in vivo source of hydroxyl radicals) with or without concurrent treatment with antioxidant enzymes will also be determined. The second and third objective are to determine the role of intracellular glutathione levels and cellular phagocytic mechanism in modulating fiber mutagenesis. The AL cell line contains only one copy of human chromosome 11 and mutations at the S1 locus coded by the MICI gene located on 11p13 can be readily scored using an antibody complement lysis assay. By using specific DNA probes of other genes that have been regionally mapped to various sites on chromosome 11, the molecular spectrum of mutations induced by chrysotile fibers and oxyradicals will be compared.